Sparkfun has the Ethernet Pro at $54.95, which also has a W5100 but is a little more slimmed down.
And if instead of an Arduino, you want a ARM Cortex-A8 board that runs Linux, has 60 digital I/Os, and built-in Ethernet, you can try the BeagleBone for $89.
Also in ARM-land is the mBED, ($50.80 from Mouser) which has built-in Ethernet but needs a carrier board with magnetics such as mbed-Xpresso Baseboard ($45.14 with LCD display and VGA out), mbed LPC1768 Workshop Development Board ($25 but barebones), or Mission Control MC-101 baseboard ($45 with lots of screw-down terminals).
Meanwhile the coolest PIC board ever is the MikroElectronica Multimedia Board for PIC32MX7 ($149) that has a touchable TFT display and SD card as well as Ethernet. MikroE also has a bunch of dedicated Ethernet boards.
Finally there is the good old Modtronix SBC65EC ($65) a PIC-based system that has Ethernet and RS-232.